The invention relates generally to apparatus associated with mast supports for sailing vessels and particularly to windsurfer mast base collars.
Dependent upon various sail sizes, it is preferable to adjust the height of a windsurfer mast. A windsurfer mast typically is a hollow metal or composite tube. The mast is slipped over a mast base which is fixed to the windsurf board. An arrangement of pulleys, jam cleats and lines are used to secure the sail, which pulls on the mast inside the sail, to the mast base.
Most mast bases have an adjustable collar fitted around them that can be releasably locked into a number of different height positions on the mast base. The lower end of the mast rests upon the collar thus determining the mast height.
There are a number of variations of mast base collars in the prior art. An early design is a simple collar which receives the ends of a steel pin into one of two pairs of notches in the interior periphery of the lower edge of the collar. The pin passes through the mast base via one set of a series of diametrically opposed hole pairs. The hole pairs are spaced vertically above one another to facilitate positioning the mast at the height desired. The disadvantage to this arrangement is that the pin can easily be lost in the water or on a sandy beach because it is independent of the collar itself. Furthermore, adjustment of the mast height demands the use of two hands on the collar and the pin. Also, the placement of the pin at a different height often proves frustrating since careful alignment of the pin through the hollow mast is required to position the pin in an opposing hole.
An improvement on the previously described prior art is very similar. The pin is tethered by a short cord to the collar to prevent loss, and the pin is retained in the hole pair by a recess in the lower edge of the collar running around the entire interior circumference. But the problem of two handed adjustment remains along with the task of threading the pin through the hole pairs.
Another improvement on the previously described apparatus eliminates the pin. The collar is connected by hinges to a pair of downward directed arms. Each arm has an interior protrusion that passes through a hole in the collar and then engages a height adjustment hole on each side of the mast base. The pins pass the load in shear from the holes in the collar to the holes in the mast base. The device is disengaged by applying manual pressure to a secondary interior ring that elastically deforms to retract the arms. One drawback to this device is that both compression forces to deform the ring and vertical displacement forces must be applied at the same time to readjust the collar.
For another variant, the collar supports a single leaf spring with a protrusion on the interior side that engages a height adjustment hole. The collar then slides down over the leaf spring to lock the protrusion in place. A disadvantage to this apparatus is the necessity to raise the collar and mast approximately three quarters of an inch to unlock the leaf spring, and, to set the collar, the mast must be extended three quarters of an inch beyond the desired location to engage the mast and collar then retract this three quarters of an inch before force can be applied.
In a further variation, the collar supports two arcuate spring biased levers that pivot about two vertically disposed pins retained by the collar. Each lever has a protrusion that engages a hole in the mast base. A drawback to this apparatus is that each lever must be independently biased away from an engaged position with a finger and, at the same time, a vertical displacement force must be applied to the collar to adjust it to a new position.
In still another variant, the collar supports two semicircular yokes. The yoke ends are supported by a pair of diametrically opposed horizontal hinge pins retained by the collar. Each yoke has an inward extending protrusion at the midpoint of its length. The yokes are spring biased to urge the protrusions into a pair of height adjustment holes. When a downward load on the mast and sail is exerted upon the collar, the geometry of the active and resultant force vectors creates a force couple that tends to rotate the yokes into a locked position. There are several disadvantages to this apparatus. First, to balance the vertical loads, the geometry of the apparatus generates significant force components in the horizontal plane. Those excessive horizontal forces require that the structure of the collar, yokes and the mast base be heavier gauge materials than would be necessary if the horizontal force components were lower. Secondly, the yokes are subjected to high level tensile forces which can deform the yokes from their preferred semi-circular shape. Thirdly, the hinge pins must transfer the high horizontal force components so they too must be of a heavier gauge than would otherwise be required. Lastly, the upper surface of the detent pin, which causes the pin to retract when an upward force is applied to the collar, takes on an angle which is unfavorable to the release movement when the detent swings out of position.